HVDC hybrid circuit breakers, such as disclosed in WO 2011/057675, are typically based on a combination of a solid-state main breaker connected in parallel to a series-connection of a solid-state auxiliary breaker and a mechanical disconnector. The principal of operation of a hybrid circuit breaker is that the main breaker, the auxiliary breaker, and the disconnector are closed during normal operation. If a trip signal is received, the hybrid circuit breaker attempts to break the current flowing through it by first opening the auxiliary breaker, thereby commutating the current flowing through the auxiliary breaker and the disconnector to the main breaker. Subsequently, the disconnector is opened for disconnecting the auxiliary breaker, and finally the main breaker is opened, resulting in a commutation of the current from the main breaker to a surge arrester connected in parallel to the main breaker.
Frequently, hybrid circuit breakers are supplied with snubber circuits in order to suppress voltage transients which arise in response to the sudden interruption of the current when the disconnector is opened. A snubber circuit typically comprises a capacitor which is connected in parallel to the auxiliary breaker.
When the breaking operation of the hybrid circuit breaker is initiated by opening the auxiliary breaker, the snubber capacitor is charged, but as soon as the current commutates from the auxiliary breaker to the main breaker, the capacitor is discharged through the disconnector and the main breaker. This discharging process, and the resulting non-zero current through the disconnector, hinders the breaking operation of the disconnector.